Numerical investigation of flow field over four in-line circular cylinders for different spacing ratio

The objective of this paper is to study the effect of spacing ratio on the wake dynamics in an inline arrangement of four cylinders. Different spacing ratios, defined as ratio of distance between center of two cylinders and diameter of cylinder, are considered while. Reynolds number (Re) kept constant. At the chosen Re, far wake is expected to transition to turbulence, and hence kappa-omega SST turbulence model is used for turbulence closure. The flow field and associated surface properties such as drag and lift force are strong function of spacing ratio. In the numerical solutions it is observed that, two counter rotating vortices are formed in the gap between the cylinders. These two vortices found to move towards downstream as the spacing ratio is increased. Also, the size of the vortices found increased. The two counter rotating vortices appears symmetric near cylinders, and hence lift coefficient observed to be very low for the first three cylinders. Lift coefficient observed on fourth cylinder found to one order of magnitude higher. The drag coefficient for all cylinders found to be positive except for the second cylinder which has negative drag for all spacing ratios.